National Institute Of Materials Physics - Romania

In this work, the effects of graphene oxide (GO) concentrations (1.5 wt.%, 2.5 wt.%, and 5 wt.%) on the structural, morphological, optical, and luminescence properties of zinc oxide nanorods (ZnO NRs)/GO nanocomposites, synthesized by a facile hydrothermal process, were investigated. X-ray diffraction (XRD) patterns of NRs revealed the hexagonal wurtzite structure for all composites with an average coherence length of about 40-60 nm. A scanning electron microscopy (SEM) study confirmed the presence of transparent and wrinkled, dense GO nanosheets among flower-like ZnO nanorods, depending on the GO amounts used in preparation. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) absorption spectroscopy, and photoluminescence (PL) measurements revealed the impact of GO concentration on the optical and luminescence properties of ZnO NRs/GO nanocomposites. The energy band gap of the ZnO nanorods was independent of GO concentration. Photoluminescence spectra of nanocomposites showed a significant decrease in the intensities in the visible light range and red shifted suggesting a charge transfer process. The nanocomposites' chromaticity coordinates for CIE 1931 color space were estimated to be (0.33, 0.34), close to pure white ones. The obtained results highlight the possibility of using these nanocomposites to achieve good performance and suitability for optoelectronic applications.

GeSn alloys have the potential of extending the Si photonics functionality in shortwave infrared (SWIR) light emission and detection. Epitaxial GeSn layers were deposited on a relaxed Ge buffer on Si(100) wafer by using high power impulse magnetron sputtering (HiPI-MS). Detailed X-ray reciprocal space mapping and HRTEM investigations indicate higher crystalline quality of GeSn epitaxial layers deposited by Ge HiPI-MS compared to commonly used radio frequency magnetron sputtering (RF-MS). To obtain a rectifying heterostructure for SWIR light detection, a layer of GeSn nanocrystals (NCs) embedded in oxide was deposited on the epitaxial GeSn one. Embedded GeSn NCs are obtained by cosputtering deposition of (Ge1-xSnx)(1-y)(SiO2)(y) layers and subsequent rapid thermal annealing at a low temperature of 400 degrees C. Intrinsic GeSn structural defects give p-type behavior, while the presence of oxygen leads to the n-character of the embedded GeSn NCs. Such an embedded NCs/epitaxial GeSn p-n heterostructure shows superior photoelectrical response up to 3 orders of magnitude increase in the 1.2-2.5 mu m range, as compared to performances of diode based only on embedded NCs.

The effects of 4-(2-hydroxyphenyl)-2-(morpholin-4-yl)-1,3-thiazole (Pr02), 1-(3,5-dibromo-2-hydroxyphenyl)-1-oxoethan-2-yl-N,N-diethyldithiocarbamate (Pr04) and 1-(5-bromo-2-hydroxy-3-methylphenyl)-1-oxoethan-2-yl-O- ethyl xanthate (Pr06) on the aqueous oxidation of chalcopyrite (CuFeS2) in air-equilibrated solution at a temperature of 25 degrees C and a pH of 2.5 were studied. The effects were investigated by using potentiodynamic polarization, electro-chemical impedance spectroscopy (EIS), scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) analysis, aqueous batch experiments, Fourier transform infrared (FTIR) spectroscopy, Raman scattering and quantum chemical calculations. It is found that the anodic current densities decrease in the order of EtOH Pr02 > Pr04 > Pr06. These results, along with those of the EIS measurements, show that Pr02, Pr04 and Pr06 are effective anodic inhibitors of chalcopyrite aqueous oxidation. Both Raman scattering and FTIR spectroscopy indicate that the elemental sulfur, polysulfide and ferric oxyhydroxides that form on the surface of the mineral are not responsible when it comes to the aqueous oxidation inhibition of chalcopyrite. Quantum chemical calculations show that the adsorption of the tested compounds on the chalcopyrite surface is energetically favorable and so, it can explain the inhibiting effects that were observed.

Industrial wastewater can be properly treated using nanotechnologies and nanomaterials. This paper presents the synthesis and characterization of three series of magnetic nanoparticles (MNPs) and corresponding thin films, used for the degradation of organic compounds and removal of heavy metals from industrial wastewater. The samples were obtained by co-precipitation from a ferric (Fe3+) and ferrous (Fe2+) ions solution in a molar ratio of 2:1, at temperatures between 80-95 degrees C. The characterization of the samples was performed by scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods. The magnetic nanoparticles were deposited on glass substrates by the centrifugal coating technique and the optical and magneto-optical activity was investigated by UV- Vis spectroscopy and magnetic circular dichroism technique (MCD). The effect of the investigated samples on the decomposition under UV irradiation of organic dyes was monitored by UV-Vis spectroscopy. Our preliminary results have shown that the magnetite and maghemite MNPs can be effective in UV degradation of methylene blue (MB) dye.

The objective of the present study is the valorization of natural resources and the recycling of vegetal wastes by converting them into novel plasmonic bio-active hybrids. Thus, a "green" approach was used to design pectin-coated bio-nanosilver. Silver nanoparticles were generated from two common garden herbs (Mentha piperitaandAmaranthus retroflexus), and pectin was extracted from lemon peels. The samples were characterized by the following methods: Ultraviolet-visible (UV-Vis) absorption spectroscopy, Fourier Transform Infrared (FT-IR), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), dynamic light scattering (DLS), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM)-Energy-dispersive X-ray Spectroscopy (EDX), and zeta potential measurements. Microscopic investigations revealed the spherical shape and the nano-scale size of the prepared biohybrids. Their bioperformances were checked in terms of antioxidant and antibacterial activity. The developed plasmonic materials exhibited a strong ability to scavenge short-life (96.1% divided by 98.7%) and long-life (39.1% divided by 91%) free radicals. Microbiological analyses demonstrated an impressive antibacterial effectiveness of pectin-based hybrids againstEscherichia coli. The results are promising, and the obtained biomaterials could be used in many bio-applications, especially as antioxidant and antimicrobial biocoatings.

In this study, we report on the structural, magnetic, and optical properties of Tb3+-doped CeF(3)nanocrystals prepared via a polyol-assisted route, followed by calcination. X-ray diffraction analysis and electron microscopy investigations have shown the formation of a dominant Ce(0.75)F(3)nanocrystalline phase (of about 99%), with a relatively uniform distribution of nanocrystals about 15 nm in size. Magnetization curves showed typical paramagnetic properties related to the presence of Ce(3+)and Tb(3+)ions. The magnetic susceptibility showed a weak inflexion at about 150 K, assigned to the cerium ions' crystal field splitting. Under UV light excitation of the Ce(3+)ions, we observed Tb(3+)green luminescence with a quantum yield of about 20%.

Antibacterial cerium-doped hydroxyapatite (Ce-HAp) layers have been researched sparingly in recent years. The Ce-HAp powder, Ca10-xCex(PO4)(6)(OH()2)with x(Ce)= 0.05, was obtained by an adapted chemical co-precipitation method at room temperature. The target was prepared using the Ce-HAp (x(Ce)= 0.05) powder sintered in air at 600 degrees C. The coatings on the Ti substrate were generated in plasma using a radio frequency (RF) magnetron sputtering discharge in an Ar gas flow in a single run. To collect the most complete information regarding the antimicrobial activity of cerium-doped hydroxyapatite with x(Ce)= 0.05, (5Ce-HAp), antimicrobial studies were carried out both on the final suspensions and on the coated surfaces. The target was tested using ultrasound measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), glow-discharge optical emission spectroscopy (GDOES), and X-ray photoelectron spectroscopy (XPS). The present study exhibited for the first time results of the homogeneous coatings of hydroxyapatite doped with cerium using a radio frequency magnetron sputtering technique. In addition, this study highlighted for the first time the stability of the cerium-doped hydroxyapatite gels used in the creation of the coating. Ultrasound measurements on the concentrated suspension of 5Ce-HAp showed a good stability compared to double distilled, water which was chosen as the reference fluid. Particles with spherical shape were observed by both TEM and SEM analysis. The broadening of the IR bands in the IR spectrum of the 5Ce-HAp film in comparison with the IR spectrum of the precursor target indicate the formation of interlinked bonds into the layer bulk. XPS analysis revealed that the mixture of Ce(3+)and Ce(4+)ions in the hydroxyapatite (HAp) structure of the coatings could be due to the deposition process. The surface of 5Ce-HAp coatings was homogenous with particles having a spherical shape. A uniform distribution of all the constituent elements on the surface the 5Ce-HAp layer was revealed. The antimicrobial assays proved that both 5Ce-HAp suspensions and 5Ce-HAp coatings effectively inhibited the development of colony forming units (CFU) for all the tested microbial strains. Moreover, the antimicrobial assays emphasized that the 5Ce-HAp suspensions had a biocide effect against Escherichia coli (E. coli) andCandida albicans(C. albicans)microbial strains after 72 h of incubation.

A simple dip coating procedure was used to prepare the magnesium doped hydroxyapatite coatings. An adapted co-precipitation method was used in order to obtain a Ca25-xMgx(PO4)(6)(OH)(2), 25MgHAp (x(Mg)= 0.25) suspension for preparing the coatings. The stabilities of 25MgHAp suspensions were evaluated using ultrasound measurements, zeta potential (ZP), and dynamic light scattering (DLS). Using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) information at nanometric resolution regarding the shape and distribution of the 25MgHAp particles in suspension was obtained. The surfaces of obtained layers were evaluated using SEM and atomic force microscopy (AFM) analysis. The antimicrobial evaluation of 25MgHAp suspensions and coatings on various bacterial strains and fungus were realized. The present study presents important results regarding the physico-chemical and antimicrobial studies of the magnesium doped hydroxyapatite suspensions, as well as the coatings. The studies have shown that magnesium doped hydroxyapatite suspensions prepared withx(Mg)= 0.25 presented a good stability and relevant antimicrobial properties. The coatings made using 25MgHAp suspension were homogeneous and showed remarkable antimicrobial properties. Also, it was observed that the layer realized has antimicrobial properties very close to those of the suspension. Both samples of the 25MgHAp suspensions and coatings have very good biocompatible properties.

In this work, new optical properties of composites based on polystyrene (PS) microspheres and graphene oxide (GO) are reported. The radical polymerization of styrene in the presence of benzoyl peroxide, pentane and GO induces the appearance of new ester groups in the PS macromolecular chains remarked through an increase in the absorbance of the infrared (IR) band at 1743 cm(-1). The decrease in the GO concentration in the PS/GO composites mass from 5 wt.% to 0.5 wt.% induces a diminution in the intensities of the D and G Raman bands of GO simultaneous with a down-shift of the D band from 1351 to 1322 cm(-1). These variations correlated with the covalent functionalization of the GO layers with PS. For the first time, the photoluminescent (PL) properties of PS/GO composites are reported. The PS microspheres are characterized by a PL band at 397 nm. Through increasing the GO sheets' concentration in the PS/GO composite mass from 0.5 wt.% to 5 wt.%, a PS PL quenching process is reported. In addition, in the presence of ultraviolet A (UVA) light, a photo-degradation process of the PS/GO composite having the GO concentration equal to 5 wt.% is demonstrated by the PL studies.

This work involves the synthesis and characterization of Cu2ZnSnS4 (CZTS) layers. The films were prepared on Mo/glass substrates by single-step electrodeposition method followed by sulfurization at 500 degrees C under argon flow. The effect of boric acid concentration on the crystallographic structure, compositional and morphological properties of CZTS films was investigated, with the objective to understand the growth behavior and to enhance the film properties. Cyclic Voltammetry was used in order to estimate the adequate deposition potential for the CZT alloy. The x-ray diffraction analysis showed the formation of the kesterite phase in all the samples. The Raman and x-ray photoelectron spectroscopy studies confirmed the existence of the CZTS phase. The scanning electron microscopy was employed to inspect the films structure. The results indicated that increasing the concentration of boric acid affects the physico-chemical properties of the films.